1. Field of the Invention
The present invention relates to a data symbol reader for reading coded data symbols, such as a bar code.
2. Description of the Related Art
In recent years, information regarding goods (e.g., the price of goods) has often been coded in the form of a bar code to be read by a bar code reader for use in a POS (point of sale) system. However, since the reading of a bar code has to be done in such a way as to scan the bar code in an arranged direction thereof one-dimensionally, a small-sized bar code cannot carry much information.
Recently a data symbol (two-dimensional data symbol) which can carry much more information than the conventional bar code, and a data symbol reader for reading such a data symbol, have been developed. One type of data symbol is formed as a black-and-white mosaic-like pattern in which black and white squares are two-dimensionally arranged.
Two types of such a data symbol reader are known. One of the types reads the pattern of a data symbol two-dimensionally at once, using an image pick-up device such as a CCD sensor (area sensor). The other type reads the pattern of a data symbol two-dimensionally by scanning the pattern line by line in a main-scanning direction while shifting the reading head in a sub-scanning direction relative to the pattern, using a line sensor.
The former type of data symbol reader, namely the one using an image pick-up device, has been receiving more attention than the latter type since the former type does not require the reading head to move relative to the data symbol to read the same. This is advantageous since the data symbol reader can read the data symbol in a short period of time.
FIG. 7 shows a conventional data symbol reader 100 using an image pick-up device, and FIG. 8 shows a condition where a reading head (head portion) 103 of the data symbol reader 100 is placed on a two-dimensional data symbol 38 for the purpose of reading the same.
As shown in FIG. 7, the data symbol reader 100 has a casing 101 which forms a general shape of the data symbol reader 100 and in which a reading device 102 including an image-pick-up device (not shown) is accommodated. The casing 101 is provided with a grip portion 107, and a head portion 103 which is formed integral with the front end of the grip portion 107. The reading device 102 is arranged in the vicinity of the head portion 103. The head portion 103 is provided at a lower end thereof with a substantially square opening 104 which determines a substantially square-shaped reading area 360 where the data symbol 38 can be read by the data symbol reader 100 when positioned therein. Accordingly, when reading the data symbol 38, it is necessary for the head portion 103 of the data symbol reader 100 to be placed on the data symbol 38 such that the data symbol 38 lies within the opening 104.
In such a positioning operation, in the case where an edge 105 of the head portion 103 covers a part of the data symbol 38 as shown in FIG. 8, the data symbol 38 cannot be properly read by the data symbol reader 100, thus resulting in a reading error.
Since the casing 101 is usually made of an opaque material it is difficult to visually check the position of the opening 104 relative to the data symbol 38 once the data symbol 38 is covered by the head portion 103. Even if it is visually checked that the data symbol 38 is not protruding from an outer edge 106 of the edge 105 of the head portion 103, a reading error will occur in the case of a condition as shown in FIG. 8.
Due to such a drawback, it is sometimes the case that the reading operation needs to be repeated, which does not efficiently utilize the above-mentioned advantage of the data symbol reader using an image pick-up device.